Inclusion of a suite of weathering tracers in the cGENIE Earth system model – muffin release v.0.9.23

Abstract

Abstract. The metals strontium (Sr), lithium (Li), osmium (Os) and calcium (Ca), together with their isotopes, are important tracers of weathering and volcanism – primary processes which shape the long-term cycling of carbon and other biogeochemically important elements at the Earth's surface. Traditionally, because of their long residence times in the ocean, isotopic shifts in these four elements observed in the geologic record are almost exclusively interpreted with the aid of isotope-mixing, tracer-specific box models. However, such models may lack a mechanistic description of the links between the cycling of the four metals to other geochemically relevant elements, particularly carbon, or climate. Here we develop and evaluate an implementation of Sr, Li, Os and Ca isotope cycling in the Earth system model cGENIE. The model offers the possibility to study the dynamics of these metal systems alongside other more standard biogeochemical cycles, as well as their relationship with changing climate. We provide examples of how to apply this new model capability to investigate Sr, Li, Os and Ca isotope dynamics and responses to environmental change, for which we take the example of massive carbon release to the atmosphere.

Trace-metal isotope 'fingerprints' of past solid Earth-ocean interactions

“…We make only one change here from the model setup of Adloff et al (2021). In Adloff et al (2021), silicate weathering contributions were split into Ca-and Mg-bearing silicates, meaning that only a part of the alkalinity supply from silicate weathering was accompanied by Ca ion input.…”

“…We make only one change here from the model setup of Adloff et al (2021). In Adloff et al (2021), silicate weathering contributions were split into Ca-and Mg-bearing silicates, meaning that only a part of the alkalinity supply from silicate weathering was accompanied by Ca ion input. Because climate change drives variations in silicate weathering in the model, while alkalinity is only removed in association with Ca and abyssal Mg-Ca exchange remains at a constant prescribed value (the model has no temperature-dependency for MgCO 3 deposition and Mg-Ca exchange at the seafloor), long-lasting perturbations could create large ion imbalances which would prevent the equilibration of the marine alkalinity and Ca reservoirs.…”

“…We ran two series of experiments using the Adloff et al (2021) pre-industrial configuration of C and metal cycling (adjusted as described above). In the first experiment series (A), we prescribed step-changes of various boundary conditions to assess the potential of different geological processes to cause long-term shifts in the isotopic composition of dissolved metals and C in seawater.…”

“…While interpreting each proxy system independently is very flexible in its application, a reductionist approach cannot capture these biogeochemical links between elemental cycles, which complicarbonate a fully internallyconsistent mechanistic understanding of metal and C isotope records. To guide the multiproxy interpretation of past interactions between the ocean, atmosphere and solid Earth, we employ the intermediate-complexity Earth system model cGENIE, which incorporates representations of the global cycles of Ca, Sr, Os, Li and C and their isotopes (Adloff et al, 2021). Using this model, we simulate a series of idealized steady state and transient responses to various plausible past changes in solid Earth interactions and explore the potential for creating paleo-event 'fingerprints'.…”

“…We use cGENIE combined with modules accounting for climate-sensitive continental weathering fluxes and marine sedimentary burial and dissolution in order to account for key processes regulating ocean chemistry on geological timescales (Ridgwell et al, 2007, Ridgwell and Hargreaves, 2007, Colbourn et al 2013. In addition to the C cycle and C isotopes (Kirtland Turner and Ridgwell, 2016), the model includes representations of the main oceanic sources and sinks of Sr, Ca, Li and Os as well as their associated main proxy-relevant isotopes that we make use of here (see Adloff et al, 2021 for a comprehensive model description and evaluation).…”